In high doses, UVB is also harmful. We have to limit exposure to under 150Mw/square centimeter, and preferably keep it at 100.

"While excessive exposure to the shorter UVA ( (that is, referring to the shortest wavelegths within the UVA spectrum. UVA is not shorter than UVB) UVA wavelengths can be dangerous (UVA wavelengths being longer, penetrate deeper into the layers of iguana skin), causing blindness, skin damage, immune dysfunction, and even death, !moderate exposure is beneficial! In diurnal reptiles, it increases activity levels, promotes basking and feeding and, through its influence on the pineal gland, can positively affect reproductive cycles in some species."

From Melissa Kaplan's Catch the Wave Article on UV Light.

Now, if we have a way to safely increase the colors our iguanas can see, why not provide it?